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Schmidtea mediterranea: a system for comparative studies of embryogenesis and regeneration

Regeneration, the replacement of lost or damaged tissues to restore organ function, remains one of the most poorly understood processes in developmental biology. The origin and regulation of cells that make regeneration possible in different systems are largely obscure. How similar or distinct developmental processes are during embryogenesis and regeneration remains to be determined. In fact, few experimental systems are available to systematically study these issues. Here, we lay the foundation for formal comparison of molecular processes and gene function during embryogenesis and regeneration in S. mediterranea (Smed), a free-living freshwater planarian species uniquely suited to address the relationship between developmental plasticity and regeneration competency.

Smed flatworms are bilaterally symmetric, triploblastic animals that possess a wide variety of differentiated cell types and organ systems. Smed are stable diploids that exist as two biotypes: asexual animals that reproduce by fission, and obligate cross-fertilizing hermaphrodites that reproduce sexually (Newmark and Sánchez Alvarado, 2002; Newmark et al., 2008). Smed embryos are direct developers: newborn hatchlings grow and mature into adult worms without an intervening larval stage (Sánchez Alvarado, 2003). At hatching, juveniles are sexually immature but otherwise possess a body plan grossly similar to the adult hermaphrodite (Sánchez Alvarado, 2003; Wang et al., 2007). These flatworms are renowned for their remarkable regenerative potential: following amputation, small tissue fragments from adult worms of either biotype re-form complete, properly patterned individuals within one to two weeks. Regeneration is dependent on neoblasts, an abundant, cycling somatic cell population comprised of pluripotent stem cells and lineage-primed progenitors. All differentiated tissues in adult planaria, including the germline, are maintained and re-made from neoblast progeny.

The Sánchez Alvarado laboratory at the Stowers Institute for Medical Research is pioneering efforts to study Smed embryogenesis. This website accompanies our manuscript, “Embryonic origin of adult stem cells required for tissue homeostasis and regeneration,” and contains the molecular staging series and molecular fate mapping atlas for Smed embryogenesis described in our publication.

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To learn more about the Smed sexual biotype and our planarian culturing conditions, please visit the “About our worms” page.